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Turf, Soil Needs Aerification
to
Combat Compaction
Sports turf typically gets much
heavier use than commercial or residential turf areas but each may suffer the
effects of compaction that results from traffic. Soil particles are squeezed
together with the upper 3/4 to 1-1/2 inches of soil becoming the most compacted.
This condition resists water penetration and limits the effectiveness of
top-applied fertilizers.
Mergenthal's plan to adapt army surplus equipment for turf aeration appeared to work until he noticed an excessive buildup of iron in the soil.
The problem goes much further: the
relationship between air, soil and water is upset. Roots need oxygen for
healthy growth but compacted soil holds built-up carbon dioxide and prevents
oxygen infusion. Roots lose their ability to absorb the water and nutrients that
may still be available in the packed soil. This is especially problematic in
short-rooted turf grasses that must rely on the top few inches of soil for
nutrition.
Compaction and ThatchWhen a soil compaction condition is
accompanied by excessive thatch buildup, as is almost always the case in poorly
maintained turf, each condition contributes to the effect of the other. When
thatch exceeds about 1/2 inch of undecomposed material, it acts as a barrier to
water and air infiltration into the soil below and will provide an environment
encouraging turf diseases and harmful insects. Compacted soils, on the other
hand, are subject to greater temperature extremes than loose soils, because of
limited air movement; microbial activity necessary to thatch decomposition is
reduced or halted.
Water that cannot penetrate the soil
runs off or accumulates in low spots where it harbors fungus growth.
Alleviating either condition will help,
but only when thatch is kept under control and the soil is properly aerified
will turf have the best chance for healthy, vigorous growth and disease
resistance.
What To Do
Dethatching and aerifying should be
done as part of the same process. Once the soil has been deeply, slowly watered
to about a 6-inch depth to soften the compaction then:
- mow with a dethatching mower
- rake off the thatch
- aerify
- test soil (pH, etc.)
- fertilize as needed
- irrigate.
Dethatching
mowers use a horizontal, rotating bar with vertically arranged cutters that
slice the interwoven network of dead and living grass plants. The resulting
short lengths of this material are loosened and brought up from the base of the
live grass stalks where they can be raked away.
Aerifying—known commonly as
aerating—may be done with a variety of devices. What they should all have
in common is the ability to draw cores from the turf. Generally, the core depth
is 3 to 4 inches and the core diameters vary between 1/4 and 5/8 inch. The core
holes in the turf should be spaced about 2 inches apart. Perhaps the best
machine for working large areas is a piston driven aerator that thrusts the core
cutters vertically. Direct up and down coring leaves a clearly defined hole.
Drum-type roller aerators will work but may cause tearing damage to the
remaining grass since this type of cutter enters the turf at one angle, moves in
an arc with the drum movement, and is withdrawn at a different angle.
Aerators must pull a core from the
soil. Merely piercing the soil does not have the same beneficial effect. The
benefits of aerifying turf include:
- improved water absorption
- exchange of CO2 and oxygen
- better placement of fertilizer
- loosened soil texture
- decomposition of remaining thatch particles
- improved germination of reseeded and overseeded turf
- revitalized, deeper, healthier root systems
- better success at introducing top dressings
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